1. Field of the Invention
The present invention relates to compositions for external application comprising as an effective ingredient kojic acid or a kojic acid derivative which can inhibit erythema or pigmentation on the skin and prevent coloration of the compositions after external application.
2. Prior Art Statement
As substances for preventing formation of melanin on human skin, kojic acid and kojic acid derivatives are known. Skin coating agents comprising these substances as effective ingredients are also known. For example, these are whitening cosmetics comprising kojic acid as a whitening component (Published Unexamined Japanese Patent Application No. 3538/78 and Published Examined Japanese Patent Application No. 18569/81), whitening cosmetics comprising aliphatic carboxylic acid diesters of kojic acid or aliphatic carboxylic acid mono-esters of kojic acid as whitening components (Published Examined Japanese Patent Application Nos. 60801/86 and 9722/85), whitening cosmetics comprising esters of aromatic acids such as cinnamic acid, benzoic acid, etc. of kojic acid as whitening components (Published Examined Japanese Patent Application No. 10005/85), ointments for preventing formation of melanin comprising kojic acid as an effective ingredient (Published Examined Japanese Patent Application No. 10447/86), etc.
Further in order to prevent coloration of the kojic acid due to the passage of time, there are known cosmetics comprising kojic acid having formulated therein 2-hydroxy-benzophenone compounds (Published Unexamined Japanese Patent Application No. 108804/87).
As described above, kojic acid and a kojic acid derivative are extremely excellent substances that can inhibit the formation of melanin; the substances are known as skin coating agents used in cosmetics. When the substances are incorporated into cosmetics and skin agents for external application and applied to the skin, the substances exhibit the excellent effects of whitening and inhibiting the formation of melanin, and cause no irritation to the skin.
Even though pigmentation such as chloasma or the like is improved by the action of kojic acid, however, pigmentation once cured sometimes reverts to its original state due to the effects of ultraviolet rays when exposed to direct rays of the sun.
It is also pointed out that when the skin is exposed to strong outdoor direct rays of the sun with these agents for external application applied to the skin, the agents for external application are sometimes colored.